I am travelling to Vietnam and Cambodia later this year and want to use US Dollars in both countries. I know that many places in Udon are happy to buy US Dollars but will not sell them. Can anyone recommend a place that will sell US Dollars, preferably with a fair exchange rate!

Four years ago I cashed in some Thai baht at the Bangkok Bank for several hundred U.S. dollars with no fuss. I did this inside the bank, not at an exchange window. Did not give it a thought at the time. Is it different now?

Yeah, like lone Star said..Gold shops. My shop does not do all the stupid passport copies. BS.
Inside the Tesco in Ud Town is a exchange window. I paid 3,100tb for a piece of worthless US , counterfiet paper, that most countries don't want anymore. Hehe. gave it to a "falong" trying to make his way back to where he came from. So sad.